Tsunami relics in the coastal landscape west of Lisbon, Portugal

Lisbon and the mouth of the river Tagus (Tejo) are known to have suffered from the great earthquake and tsunami of November 1st, 1755. Whereas historical sources mention tsunami waves and describe inundation in Lisbon, field evidence from this event has been found only along the Algarve coast and the Spanish Atlantic coast in the south. Our observations in the Cabo da Roca-Cascais area west of Lisbon resulted in the discovery of several very significant tsunami relics in the form of single large boulders, boulder ridges, pebbles and shells high above the modern storm level. Deposition of large amounts of sand by the tsunami waves has intensified eolian rock sculpturing. Abrasion of soil and vegetation still visible in the landscape may point to the great Lisbon event of only some 250 years ago, but radiocarbon and ESR datings also yielded older data. Therefore, we have evidence that the Portuguese coastline has suffered more than one strong tsunami in the Younger Holocene.